by Michael King, William M. Welch and John Bacon, USA TODAY

by Michael King, William M. Welch and John Bacon, USA TODAY

DECATUR, Ga. - A 911 tape released Wednesday reveals the courageous efforts of a bookkeeper who talked a gunman into putting down his weapon after he walked into her elementary school with an automatic rifle and almost 500 rounds of ammunition.

Michael Brandon Hill, 20, is accused of opening fire in the Atlanta-area school Tuesday. Antoinette Tuff spoke to Hill while on the phone with the 911 operator. She said Hill said he was off his medication and that "he don't care if he dies, he don't have nothing to live for," Tuff told the operator. "He said he's not mentally stable."

Later, she talked him into surrendering.

"He's laying on the floor. He's got everything out of his pockets. There isn't anything. The only thing he has is his belt. Everything is out of his pockets. Everything is sitting here on the counter, so all we need to do is they can just come in, and I'll buzz them in."

When the situation had ended, Tuff finally broke down.

"I'm going to tell you something baby - I've never been so scared in all the days in my life," she told the dispatcher.

Authorities were still trying to determine why Hill fired at least six shots with an assault rifle at Ronald E. McNair Discovery Learning Academy on Tuesday. Police returned fire; no one was injured.

Investigator T.L. Wortham of the DeKalb County Sheriff Department's Fugitive Unit told WSB-TV that as officers were apprehending the suspect, he said, "I'm sorry, I'm off my meds." Several weapons were seized, Wortham said.

Hill faces charges including aggravated assault on a police officer, terroristic threats and possession of a firearm by a convicted felon.

The suspect was arrested early this year for threatening to kill his brother. A police report from Henry County Police shows that he was taken into custody on Mar. 13 and charged with terroristic threats.

Hill's brother, Timothy Hill, told police in late December 2012 that the suspect sent him a Facebook message saying "that he would shoot him in the head and not think twice about it," according to the police report.

Timothy Hill, 22, told ABC News on Wednesday that the suspect has "long history of medical disorders" including bipolar disorder, and was bound to "do something stupid." Hill said he's not close to his brother and that Michael Hill was taking drugs for attention-deficit hyperactivity disorder as early as age 6.

"I had a feeling he was going to eventually, one day, do something stupid, but not of this magnitude," he told ABC News.

The elementary school of 870 students up to fifth grade is named for an astronaut who died aboard Challenger, the space shuttle that exploded after takeoff in 1986. Students returned to classes Wednesday, but they were held at a nearby high school.

DeKalb County Police Chief Cedric Alexander said the McNair school has a system requiring visitors to be cleared and buzzed in, and the gunman gained entry by slipping in behind someone authorized to enter. He said the man did not get past the school's main office.

King reports for WXIA TV in Atlanta. Welch reported from Los Angeles. Contributing: The Associated Press.